Michael Levin defends compatibilism against the charge that special relativity implies what he calls relativistic fatalism.

The notion that special relativity can show that the world is deterministic was first proposed by the philosophers C. W. Rietdijk and Hilary Putnam in the 1960's. J.J.C.Smart described a "block universe," in which all space-time events already exist, as a "tenseless" deterministic universe.

Levin cites Michael Lockwood's 2005 book, The Labyrinth of Time, as arguing "with new vigor that the Special Theory of Relativity rules out free will."

Lockwood argues that this is not just a case of causal determinism denying free will. Special relativity, he says, challenges the very notion of cause. If the future is already out there, Lockwood says, causality has little to do with it.

Levin disagrees. He says that special relativity (SR) has room for cause and effect.

Relativistic fatalists...are certainly not compelled to renounce causality by SR alone, which respects standard conditions on the time order of cause and effect. They may therefore find it less disruptive to adopt a non-Aristotelian account of causality consonant with SR, such as energy transmission, and confront compatibilism restated in its terms. Moreover, denial of causality wars with their larger goal, shared by all fatalists, of showing that people are far more constrained than ordinarily supposed. If nothing is causally impossible — causality being an illusion — people are less constrained than ordinarily supposed. From the fatalist's own viewpoint, Lockwood's argument proves too much.
("Compatibilism and Special Relativity," J. Phil, CIV, 9, p.439, 2007)

Compatibilists hold that freedom depends on how, not whether, behavior is caused, in particular, on the causal role of preference, Levin says, and thus that

a compatibilist may argue [that] freedom is consistent with the relativistic fixity of the future. The simultaneity of my running with an event simultaneous with the onset of my desire to run is irrelevant to my running freely, on this view; what matters, as always, is whether the cause of my running is a preference. Since SR does not address the causes of human behavior, it cannot show that my running is not caused by a preference, hence cannot show that I do not run freely.
(ibid., p.434)

A relativistic fatalist will claim to be able to absorb causation by preference and all the compatibilist's pet points about ordinary usage. "So be it," the relativistic fatalist will say, "'Freedom' as ordinarily used does not require a causally indeterminate future, or a future the agent believes is causally indeterminate, only a future caused in part by the agent's wants. The core use of 'cause' may well be to denote energy flow, and no doubt energy flows unidirectionally from wants to actions in orientable space-times. The fact remains that your so-called 'future' is a done deal. As we speak, energy is flowing into 'future' time-slices of your quadriceps. No matter how the situation is described, you cannot at noon your time refrain from running at 2 your time, and looking back from 3 your time you could not have done otherwise, because you cannot refrain from what you are already doing. You compatibilists set no store by the categorical power to do otherwise, period, but the counterfactual conditionals you do think necessary for freedom are uniformly false. Lockwood fights shy of these counterfactuals, but Rietdijk boldly denied them:

I could not possibly have influenced event [R] in an arbitrary way (e.g., have prevented [R]) at any moment when [R] was still in the future, or was present, for me at [O], supposed that I did desire to do so."

Thus speaks the relativistic fatalist.
(ibid., p.445-6)

Levin appears to address the question of future contingency for libertarians. Although they think only one of the potential branching future will be actualized, and thus real, they do not see the SR sense in which it is already real.

Here is where the advantages of compatibilism over libertarianism may be most clear. It is hard to see how a libertarian can posit a plurality of possible futures, or deploy his familiar metaphors of branching paths and tree trunks gradually denuded of branches, and yet grant that in any sense one future is presently real.
(ibid., p.452)

Finally, Levin provides a memorable illustration for the special relativistic, block universe, view of the future.

Keats's Ode on a Grecian Urn has inspired comparison of space-time to a continuum of urns (with or without the natural Newtonian metric) on which figures pose in eternal stasis. Compatibilists, unfazed, consider the figures free insofar as their postures on one urn result from their desires on another. The lover reaching for the maid on urn u embraces her freely on urn u+ if he does so because on u he yearns to. With so many urns the maid will be faded on some and absent from others, hardly what Keats had in mind, but mortality is a small price for a kiss, and freedom.
(ibid., p.452)